Synthesis, crystal structure, magnetic properties and Hirshfeld surface analysis of two cobalt(II) complex anions templated by pyridinium-based cations

Two organic-inorganic hybrid salts, (C6H9N2)(2)[Co(C2O4)(2)]center dot H2O (1) and (C5H7N2)(2)[Co(C2O4)(2)(H2O)(2)] (2) (C6H9N2+ = 2-amino-3-methylpyridinium; C5H7N2+ = 4-aminopyridinium) have been obtained. Salt 1 is characterized by the formation of one-dimensional chains of the anionic complexes [Co(C2O4)(2)](2-), with the Co(II) centers located in a distorted (2 + 2 + 2) octahedral environment of six oxygen atoms from three chelating oxalato(2 -) ligands. By contrast, salt 2 features discrete anionic complexes [Co(C2O4)(2)(H2O)(2)](2-) with distorted (4 + 2) octahedral CoO6 coordination sphere formed by two bidentate O,O-donor oxalato(2 -) ligands in the equatorial plane and two aqua ligands in the axial positions. Hydrogen bonding interactions of the type O-H center dot center dot center dot O and N-H center dot center dot center dot O along with pi-pi stacking interactions between pyridine rings contribute to the stabilization of the 3-D supramolecular frameworks in 1 and 2. Temperature-dependence magnetic moment (mu) collected under zero-field cooled (ZFC) and field-cooled (FC) conditions revealed strong antiferromagnetic ordering below T-N = 25 K for 1, a behavior which is confirmed by the negative Weiss constant, theta = 27.6 K. By contrast, in 2, the Weiss constant, theta = 0 K is in line with a paramagnetic behavior. The three-dimensional Hirshfeld surface (3D-HS) analysis and the two-dimensional fingerprint plots (2D-FP) revealed that in 2, the structure is dominated by H center dot center dot center dot O/ H center dot center dot center dot O and H center dot center dot center dot H contacts.